A gas turbine engine may be used to power various types of vehicles and systems. A particular type of gas turbine engine that may be used to power aircraft is a turbofan gas turbine engine. A turbofan gas turbine engine may include, for example, five major sections, a fan section, a compressor section, a combustor section, a turbine section, and an exhaust section. The fan section is positioned at the front, or “inlet” section of the engine, and includes a fan that induces air from the surrounding environment into the engine, and accelerates a fraction of this air toward the compressor section. The remaining fraction of air induced into the fan section is accelerated into and through a bypass plenum, and out the exhaust section.
The compressor section raises the pressure of the air it receives from the fan section to a relatively high level. In a multi-spool engine, the compressor section may include two or more compressors. For example, in a triple spool engine, the compressor section may include a high pressure compressor, and an intermediate compressor. The compressed air from the compressor section then enters the combustor section, where a ring of fuel nozzles injects a steady stream of fuel. The injected fuel is ignited by a burner, which significantly increases the energy of the compressed air.
The high-energy compressed air from the combustor section then flows into and through the turbine section, causing rotationally mounted turbine blades to rotate and generate energy. The air exiting the turbine section is exhausted from the engine via the exhaust section, and the energy remaining in this exhaust air aids the thrust generated by the air flowing through the bypass plenum.
The exhaust air exiting the engine may include varying levels of one or more pollutants. For example, the exhaust air may include, at varying levels, certain oxides of nitrogen (NOx), carbon monoxide (CO), unburned hydrocarbons (UHC), and smoke. In recent years, environmental concerns have placed an increased emphasis on reducing these, and other, exhaust gas emissions from gas turbine engines. In some instances, emission-based landing fees are imposed on aircraft that do not meet certain emission standards. As a result, engine ownership and operational costs can increase.
Hence, there is a need for a gas turbine engine that can operate with reduced levels of exhaust gas emissions and/or that can reduce the likelihood of an owner being charged an emission-based landing fee and/or can reduce ownership and operational costs.